In recent years, as the density of electronic devices is increased and as the sizes electronic devices are reduced, printed wiring boards have been applied to a variety of uses. For example, in a hard disk drive, in which high-speed transfer of data is required, a printed wiring board is used as a substrate for a magnetic head suspension on which a magnetic head is mounted.
Patent Document 1 discloses such a printed wiring board having an insulating layer in which through hole is formed, conductive paste filling the through hole, and a conductive layer formed on either side of the insulating layer. Each conductive layer is formed of copper foil and has a predetermined wiring pattern. Since conductive paste generally has good conductivity, it is widely used for a wide variety of electronic devices. In the printed wiring board, a conductive paste in which conductive filler such as metal powder is dispersed in a binder resin such as epoxy resin is used. The conductive layers formed on both sides of the insulating layer are electrically connected to each other with the conductive paste.
Patent Document 2 discloses a printed wiring board having an insulating layer and a conductive layer formed on either side of the insulating layer. The conductive layers are electrically connected to each other with solder paste. The printed wiring board includes an insulating layer in which through hole is formed, solder paste caused to fill the through hole by reflow soldering, a conductive layer formed either side of the insulating layer. Each conductive layer has a predetermined wiring pattern. In the printed wiring board, the conductive layers formed on both sides of the insulating layer are electrically connected to each other with solder paste.
Patent Document 3 discloses a printed wiring board that is used as a substrate for a magnetic head suspension in the above described hard disk drive. The printed wiring board includes a metallic substrate made, for example, of stainless steel (SUS), an insulating layer laminated on the metallic substrate, and a conductive layer laminated on the insulating layer. The conductive layer is made of copper foil and is formed into a predetermined wiring pattern. Each layer of the printed circuit board is etched to have a predetermined shape.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2000-68620    Patent Document 2: Japanese Laid-Open Patent Publication No. 2002-94206    Patent Document 3: Japanese Laid-Open Patent Publication No. 2002-25213